The present invention relates to synthetic resin compositions and to methods of utilizing the same. More particularly, the present invention relates to synthetic resin compositions and to methods of applying such synthetic resin compositions to porous or absorbent materials and controlling their spreading, diffusing, or migrating thereon or their penetrating therein. Even more particularly, the present invention is concerned with the so-called bonded, "nonwoven" textile fabrics, i.e., fabrics produced from textile fibers without the use of conventional spinning, weaving, knitting or felting operations. Although not limited thereto, the invention is of primary importance in connection with nonwoven fabrics derived from "oriented" or carded fibrous webs composed of textile-length fibers, the major proportion of which are oriented predominantly in one direction.
Typical of such fabrics are the so-called "MASSLINN" nonwoven fabrics, some of which are described in greater particularity in U.S. Pat. Nos. 2,705,687 and 2,705,688, issued Apr. 5, 1955, to D. R. Petterson et al. and I. S. Ness et al., respectively.
Another aspect of the present invention is its application to nonwoven fabrics wherein the textile-length fibers were originally predominantly oriented in one direction but have been recognized and rearranged in predetermined designs and patterns of fabric openings and fiber bundles. Typical of such latter fabrics are the so-called "KEYBAK" bundled nonwoven fabrics, some of which are described in particularity in U.S. Pat. Nos. 2,862,251 and 3,033,721, issued Dec. 2, 1958 and May 8, 1962, respectively, to F. Kalwaites.
Still another aspect of the present invention is its application to nonwoven fabrics wherein the textile-length fibers are disposed at random by air-laying techniques and are not predominantly oriented in any one direction. Typical nonwoven fabrics made by such procedures are termed "isotropic" nonwoven fabrics and are described, for example, in U.S. Pat. Nos. 2,676,363 and 2,676,364, issued Apr. 27, 1954 to C. H. Plummer et al.
And still another aspect of the present invention is its application to nonwoven fabrics which comprise textile-length fibers and which are made basically by conventional or modified aqueous papermaking techniques such as are described in greater particularity in pending patent application Ser. No. 4,405, filed Jan. 20, 1970 by P. R. Glor and A. H. Drelich. Such fabrics are also basically "isotropic" and generally have like properties in all directions.
The conventional base starting material for the majority of these nonwoven fabrics is usually a fibrous web comprising any of the common textile-length fibers, or mixtures thereof, the fibers varying in average length from approximately 3/8 inch to about 21/2 inches. Exemplary of such fibers are the natural fibers such as cotton and wool and the synthetic or man-made cellulosic fibers, notably rayon or regenerated cellulose.
Other textile-length fibers of a synthetic or man-made origin may be used in various proportions to replace either partially or perhaps even entirely the previously named fibers. Such other fibers include: polyamide fibers such as nylon 6, nylon 66, nylon 610, etc.; polyester fibers such as "Dacron," "Fortrel" and "Kodel;" acrylic fibers such as "Acrilan," "Orlon" and "Creslan;" modacrylic fibers such as "Verel" and "Dynel;" polyolefinic fibers derived from polyethylene and polypropylene; cellulose ester fibers such as "Arnel" and "Acele"; polyvinyl alcohol fibers; etc.
These textile-length fibers may be replaced either partially or entirely by fibers having an average length of less than about 1/2 inch and down to about 1/4 inch. These fibers, or mixtures thereof, are customarily processed through any suitable textile machinery (e.g., a conventional cotton card, a "Rando-Webber," a papermaking machine, or other fibrous web producing apparatus) to form a web or sheet of loosely associated fibers, weighing from about 100 grains to about 2,000 grains per square yard or even higher.
If desired, even shorter fibers, such as wood pulp fibers or cotton linters, may be used in varying proportions, even up to 100 percent, where such shorter length fibers can be handled and processed by available apparatus. Such shorter fibes have lengths less than 1/4 inch.
The resulting fibrous web or sheet, regardless of its method of production, is then subjected to at least one of several types of bonding operations to anchor the individual fibers together to form a self-sustaining web. One method is to impregnate the fibrous web over its entire surface area with various well-known bonding agents, such as natural or synthetic resins. Such over-all impregnation produces a nonwoven fabric of good longitudinal and cross strength, acceptable, durability and washability, and satisfactory abrasion resistance. However, the nonwoven fabric tends to be somewhat stiff and board-like, possessing more of the properties and characteristics of paper or board than those of a woven or knitted textile fabric. Consequently, although such over-all impregnated nonwoven fabrics are satisfactory for many uses, they are still basically unsatisfactory as general purpose textile fabrics.
Another well-known bonding method is to print the fibrous webs with intermittent or continuous straight or wavy lines, or areas of binder extending generally transversely or diagonally across the web and additionally, if desired, along the fibrous web. The resulting nonwoven fabric, as exemplified by a product disclosed in the Goldman U.S. Pat. No. 2,039,312 and sold under the trademark, "MASSLINN," is far more satisfactory as a textile fabric than over-all impregnated webs in that the softness, drape and hand of the resulting nonwoven fabric more nearly approach those of a woven or knitted textile fabric.
The printing of the resin binder on these nonwoven webs is usually in the form of relatively narrow lines, or elongated rectangular, triangular or square areas, or annular, circular, or elliptical binder areas which are spaced apart a predetermined distance which, at its maximum, is preferably slightly less than the average fiber length of the fibers constituting the web. This is based on the theory that the individual fibers of the fibrous web should be bound together in as few places as possible.
The nominal surface coverage of such binder lines or areas will vary widely depending upon the precise properties and characteristics of softness, drape, hand and strength which are desired in the final bonded product. In practice, the nominal surface coverage can be designed so that it falls within the range of from about 10 percent to about 50 percent of the total surface of the final product. Within the more commercial aspects of the present invention, however, nominal surface coverages of from about 12 percent to about 40 percent are preferable.
Such bonding increases the strength of the nonwoven fabric and retains substantially complete freedom of movement for the individual fibers whereby the desirable softness, drape and hand are obtained. This spacing of the binder lines and areas has been accepted by the industry and it has been deemed necessarily so, if the stiff and board-like appearance, drape and hand of the over-all impregnated nonwoven fabrics are to be avoided.
The nonwoven fabrics bonded with such line and area binder patterns have had the desired softness, drape and hand and have not been undesirably stiff or board-like. However, such nonwoven fabrics have also possessed some disadvantages.
For example, the relatively narrow binder lines and relatively small binder areas of the applicator (usually an engraved print roll) which are laid down on the fibrous web possess specified physical dimensions and inter-spatial relationships as they are initially laid down. Unfortunately, after the binder is laid down on the wet fibrous web and before it hardens or becomes fixed in position, it tends to spread, diffuse or migrate whereby its physical dimensions are increased and its inter-spatial relationships decreased. And, at the same time, the binder concentration in the binder area is lowered and rendered less uniform by the migration of the binder into adjacent fibrous areas. One of the results of such migration is to make the surface coverage of the binder areas increase whereby the effect of the intermittent bonding approaches the effect of the over-all bonding. As a result, some of the desired softness, drape and hand are lost and some of the undesired properties of harshness, stiffness and boardiness are increased.
Various methods have been proposed to prevent or to at least limit such spreading, diffusing or migration tendencies of such intermittent binder techniques.
For example, U.S. Pat. No. 3,009,822, issued Nov. 21, 1961 to A. H. Drelich et al., discloses the use of a nonmigratory regenerated cellulose viscose binder which is applied in intermittent fashion to fibrous webs under conditions wherein migration is low and the concentration of the binder in the binder area is as high as 35 percent by weight, based on the weight of the fibers in these binder areas. Such viscose binder possesses inherently reduced spreading, diffusing and migrating tendencies, thereby increasing the desired softness, drape and hand of the resulting nonwoven fabric. This viscose binder has found acceptance in the industry but the use of other more versatile binders has always been sought.
Resins, or polymers as they are often referred to herein as interchangeable terms, are high molecular weight organic compounds and, as used herein, are of a synthetic or man-made origin. These synthetic or man-made polymers have a chemical structure which usually can be represented by a regularly repeating small unit, referred as a "mer," and are formed usually either by an addition or a condensation polymerization of one or more monomers. Examples of addition polymers are the polyvinyl chlorides, the polyvinyl acetates, the polyacrylic resins, the polyolefins, the synthetic rubbers, etc. Examples of condensation polymers are the polyurethanes, the polyamides, the polyesters, etc.
Of all the various techniques employed in carrying out polymerization reactions, emulsion polymerization is one of the most commonly used. Emulsion polymerized resins, notably polyvinyl chlorides, polyvinyl acetates, carboxylated styrene butadiene rubbers, and polyacrylic resins, are widely used throughout many industries. Such resins are generally produced by emulsifying the monomers, stabilizing the monomer emulsion by the use of various surfactant systems, and then polymerizing the monomers in the emulsified state to form a stabilized resin polymer. The resin polymer is usually dispersed in an aqueous medium as discrete particles of colloidal dimensions (1 to 2 microns diameter or smaller) and is generally termed throughout the industry as a "resin dispersion," or a "resin emulsion" or "latex."
Generally, however, the average particle size in the resin dispersion is in the range of about 0.1 micron (or micrometer) diameter, with individual particles ranging up to 1 or 2 microns in diameter and occasionally up to as high as about 3 or 5 microns in size. The particle size of such colloidal resin dispersions vary a great deal, not only from one resin dispersion to another but even within one resin dispersion itself.
The amount of resin binder solids in the resin colloidal aqueous dispersion varies from about 1/10 percent solids by weight up to about 60 percent by weight or even higher solids, generally dependent upon the nature of the monomers used, the nature of the resulting polymer resin, the surfactant system employed, and the conditions under which the polymerization was carried out.
These resin colloidal dispersions, or resin emulsions, or latexes, may be anionic, non-ionic, or even polyionic and stable dispersions are available commercially at pH's of from about 2 to about 11.
As will be pointed out in greater detail, such resin dispersions are used in the present inventive concept at alkaline pH ranges. Various alkaline reagents, such as ammonia, are therefore added to bring the pH out of the acid range.
The amount of resin which is applied to the porous or absorbent material varies within relatively wide limits, depending upon the resin itself, the nature and character of the porous or absorbent materials to which the resins are being applied, its intended use, etc. A general range of from about 4 percent by weight up to about 50 weight percent by weight, based on the weight of the porous or absorbent material, is satisfactory under substantially all uses. Within the more commercial limits, however, a range of from about 10 percent to about 30 percent by weight, based on the weight of the porous or absorbent material, is preferred.
Such resins have also found use in the coating industries for the coating of knitted fabrics, woven fabrics, paper, paper products, leather, and other materials. The resins are also used as adhesives for laminating films, sheets and like materials or for bonding fibrous webs. These resins have also found wide use as additives in the manufacture of paper, the printing industry, the painting industry, the decorative printing of textiles, and in other industries.
In most instances, the resin is colloidally dispersed in water and, when applied from the aqueous medium to a porous or absorbent sheet material which contains additional water is carried by the water until the water is evaporated or otherwise driven off. If it is desired to place the resin only on the surface of the wet porous or absorbent sheet material and not to have the resin penetrate into the porous or absorbent sheet material, such is usually not possible inasmuch as diffusion takes place between the aqueous colloidal resin and the water in the porous material. In this way, the colloidal resin tends to spread into and throughout the porous material and does not remain merely on its surface.
Or, if it is desired to deposit the resin in a specific intermittent print pattern, such as is used in bonding nonwoven fabrics, the aqueous colloid tends to diffuse, spread or migrate and to wick along the individual fibers and to carry the resin with it beyond the confines of the nominal intermittent print pattern. As a result, although initially placed on the nonwoven fabric in a specific intermittent print pattern, the ultimate pattern goes far beyond that due to the spreading of migration which takes place due to the diffusion of the water and the resin, until the water is evaporated or otherwise driven off.
We have discovered new resin binder compositions containing polymers colloidally dispersed in aqueous media and new methods of applying such resin binder compositions to porous or absorbent material, as enumerated herein, whereby the resins are applied in a controlled, relatively nonmigrating manner. If it is desired that the resin be placed only on the surface of the porous or absorbent material, our compositions and methods will allow this to be done. Furthermore, if it is desired that the resin be impregnated throughout the material, from one surface to the other surface, again, our compositions and methods will allow this to be done.